In recent years, a method for producing a polymer using complexes of late transition metals as a catalyst for olefin polymerization has become known.
Generally, metal complexes having a metal-hydrogen bond or metal-carbon bond have been used as a catalyst system used for coordination polymerization.
J. Am. Chem. Soc., 127, 5132 (2005) (Non-patent document 1) discloses a polymerization mechanism and a catalyst deactivation mechanism in polymerization of vinyl acetate using a metal complex of group 10 elements of the periodic table. Particularly, the document proposes β-acetoxy elimination after the vinyl acetate insertion into the metal-alkyl bond as one of the catalyst deactivation mechanisms. This shows that the metal-acetoxy complex generated by β-acetoxy elimination does not have polymerization activity and it was generally considered that the olefin insertion into the metal-oxygen bond cannot happen.
Chem. Commun., 744 (2002) (Non-patent document 2) discloses copolymerization of ethylene and methyl acrylate using the product obtained by allowing the zero-valent late transition metal and ligand to react in advance as a catalyst. In this catalyst system, it is presumed that the generation of a metal-hydride complex initiates the polymerization reaction. However, it is considered that the decomposition of the catalyst species proceeds due to the low thermal stability of the metal-hydride complex, resulting in the low polymerization activity.
J. Am. Chem. Soc., 131, 14606 (2009) (Non-patent document 3) discloses the copolymerization of ethylene and vinyl acetate using the isolated metal-methyl complex catalyst, and shows that the polymerization activity was noticeably improved in the case of using the isolated metal-methyl complex catalyst compared to the case of using a metal-hydride complex as generated in situ. However, metal-alkyl complexes generally have a problem in the stability such that they tend to decompose by the impurities during the polymerization and there was a challenge for the industrial use.